Forex Trading 2018- TA/FA- Setups and discussion, page-4227

Sorry to butt in but I actually had a similar discussion with them few weeks earlier and I was told around 6 to 9 is sufficient - although they currently trade around 60+ EA's in total.

Also like Sharks has mentioned, depends on the characteristic of your strategy - you'd want each strategy to protect against each other when things go wrong, for example if the market goes into free fall, your reversal strategy would fail in this case but your trend trading and/or breakout strategies would cover your losses.

It's recommended to start out with 3 models that would do things like above, and then slowly add other strategies like scalping, range bound trading, etc.